The invention relates to enzyme electrodes.
It has previously been proposed To employ enzyme electrodes having laminated membranes for assaying glucose and galactose as described, for example, in Clark U.S. Pat. No. 3,539,455; Newman U.S. Pat. Nos. 3,979,274 and 4,073,713; Johnson U.S. Pat. Nos. 4,220,503, 4,356,074 and 4,404,066; and Japanese Patent Appln. publication 60-185153. Such enzyme electrode assays involve measurement of the enzyme-catalyzed oxidation of glucose or galactose to generate hydrogen peroxide. On electrodes of this type the enzyme is interposed and immobilized between two membranes, the first or outer of which comes into contact with the sample to be assayed and permits access of glucose or galactose and of oxygen to the enzyme from the sample while restricting the passage of proteins, red blood cells, and other macromolecules, and the second of which is in close relationship with the face of the sensor electrode and permits access of hydrogen peroxide to the electrode while at the same time excluding passage of interfering substances having a molecular weight greater than about 250, e.g., ascorbic acid and uric acid. In practice, the sample to be assayed is brought into contact with the outer face of the first or outer membrane. The glucose or galactose in the sample diffuses through the membrane into contact with the immobilized enzyme, leading to the oxidation mentioned above, and diffusion of the resulting hydrogen peroxide through the second or inner membrane into contact with the sensor electrode causes development of an electrical current which can then be read by conventional means, thus enabling determination of the glucose or galactose concentrations by calculations based upon similar measurements made on standard solutions containing known concentrations of the glucose or galactose.